FR2640927A1 - - Google Patents

Abstract

Car braking system with the assitance of at least one braking disk or the equivalent, of which at least the friction track is made from a material such as carbon fibres whose coefficient of friction increases rapidly when the fiction track exceeds a threshhold value of Ts. It further comprises a sensor (50) designed to measure the temperature of the fiction track (18) in the pressing means (20) or immediately downstream of the latter, whereby the sensor is connected via a threshold temperature sensor (49) to a releasing means (40, 55), capable pf releasing, at least partially and in a significant manner, one (21) of two break-release means when the temperature of the friction track is in the region of, but below, said threshhold temperature (TS). Application: for highly sensitive break disks made of carbon fibres, in particular.

Description

BRAKING SYSTEM FOR A VEHICLE
The present invention relates to a braking system for a vehicle using at least one brake disc or equivalent, at least the friction track of which is made of a material such as carbon fibers, having a coefficient of friction which increases rapidly when the temperature at the friction contact exceeds a predetermined threshold value, this device comprising at least two separate brake application members but actuated simultaneously by the driver of the vehicle.

 Disc brakes have been applied to almost all vehicles and in particular to motorcycles, and a last improvement of this type of brake consisted in using carbon fiber brake discs cooperating with friction linings also in carbon fibers. This type of high performance brake, because it is light and resistant to very high temperatures, encountered difficulties in its application to motorcycles. Indeed, the coefficient of friction of the friction torque: carbon fiber linings on carbon fiber brake disc, present for temperatures of the order of 400 to 4500C called transition, d, sudden variations in the coefficient of friction which, for example by an avalanche effect, goes from 0.15 to 0 , 5 for very little additional heating of the friction surfaces in contact. In addition, in wet conditions, the coefficient of cold friction can drop below 0.1, which practically constitutes conditions for fading the brakes. The sudden appearance of a high coefficient of friction, of the order of 0.4 to 0.5, endangers the safety of motorcycles during braking, due to unavoidable wheel locks causing falls and skidding .

 The object of the present invention is precisely to propose a braking system, preferably applicable to a motorcycle but also to other types of vehicles, and which is capable of avoiding, in the vicinity of the transition temperature of the friction surfaces , that the sudden rise in the coefficient of friction does not result in a sudden increase in the braking torque, leading to the locking of the braked wheel or wheels. When applied to a motorcycle in which braking is manually actuated wheel by wheel, this braking system must also allow the driver to continuously adjust his effort in applying the brakes.

 To this end, according to the invention, the braking system further comprises a detector of the temperature of the friction track in the clamping members or immediately downstream of them and this detector is coupled, via a detector. temperature threshold, to a release member able to release at least partially and significantly one of the two brake application members, called the first brake member, when the temperature of the friction track detected by the detector threshold is close to, but less than, said threshold temperature and has triggered, via the threshold detector, a switching member.

 The release device can be any, but must be adapted to the type of brakes used (hydraulic, pneumatic, mechanical, electric). According to a first embodiment applicable to fluid pressure brakes, more particularly to hydraulic brakes, the release member is a distributor of the brake clamping fluid of said first clamping member, comprising an inlet and two outlets, one towards said first member and the other towards the discharge, an electromagnetically controlled distributor member such as a valve being able to connect said first clamping member either to a brake pressure transmitter actuated by the driver of the vehicle, or, when the switching member is triggered to excite said electromagnetic control, on discharge with closure of the input.

 According to a second embodiment applicable to fluid pressure brakes, more particularly to pneumatic brakes such as those of industrial and railway vehicles, the release member is a brake pressure divider, electrically controlled by the release member. switching, the second braking member being suppressed if necessary.

 According to another embodiment, when the brake clamping members are actuated by fluid pressure, the first clamping member has an efficiency proportional to that of the other brake clamping member called the second braking member, but greater than that of this second braking member, using any suitable means such as: greater brake cylinder cross section, greater braking pressure, friction linings with greater coefficient of friction.

According to another embodiment allowing the driver, in particular the driver of a motorcycle, to face variations in the temperature of the transition point of the friction coefficient, the switching member is adjustable by the driver of the vehicle for him allow the temperature threshold and / or the triggering threshold of the switching member to be varied. As a variant, the actuating member for controlling the first braking member can cooperate with at least one predominantly spring capable of reduce the braking pressure of the first braking member compared to that of the second braking member by a substantially constant value, the calibration of this predominant spring being, for example, adjustable by the driver.
According to another embodiment of the invention, the temperature sensor of the friction track is repelled by an elastic member in frictional contact with the friction track, immediately downstream of the first braking member which is placed - even downstream of the second braking member, relative to the normal direction of rotation of the brake disc.

 The braking system according to the invention may comprise a switching valve capable of connecting the brake pressure fluid circuit of the second braking member, either only to the second braking member, or simultaneously on the one hand to the second braking member and secondly to the first braking member, via the release member.

Other objects, characteristics and advantages will appear on reading the description of various embodiments of the invention, given without limitation and with reference to the appended drawing, where:
- Figure 1 is a fragmentary sectional view of a
motorcycle front end fitted with a sys
braking device according to the invention represented
felt in figure 2 and applied to a disc
carbon fiber brake;
- the figure is a fragmentary and schematic view of the
carbon fiber brake disc of the
figure 1 combined with a braking system
according to the invention with two drawers
different rage.

 The front end of a motorcycle shown in FIG. 1 comprises, in particular, a single suspension arm 1 which carries, by means of ball or roller bearings 4a and 4b, a rotary tubular axis 3 tightened on the bearings 4a, 4b by a nut 5. The hub 6 of a wheel 7 which has a rim 8 on which a pneumatic tire 9 is mounted, is tightened on a reinforced part 3a of the rotary axis 3 by a nut 10 so as to achieve coupling in rotation with us, on the one hand the heads ll of screws 12 screwed into the hub 6 of light alloy and, on the other hand, the teeth 13 of a flange 14 secured to the tubular axis 3. The heads ll of the screws 12 are coupled at their periphery to a rigid flange 15 in the shape of a bell and which supports, by a cylindrical crown 1o provided with external splines 17, a brake disc 18 made of carbon fibers and relatively thick (its minimum thickness is greater than 1 cm).

 The brake disc 18 slides axially by its internal grooves 19 on the grooves 17 of the crown 16 and is overlapped by a single brake caliper 20 which is rotatably mounted by needle bearings 2 on the single suspension arm 1 and which is prevented from rotating by a retaining link (not shown).

 The caliper 20 has two brake cylinders 21, 22, in each of which is provided a bore with an axis perpendicular to the friction surface of the disc 18 and inside which moves, in sealed manner, a respective brake piston (in the sectional view, only the bore 23 and the piston 24 appear). The respective pressure chambers delimited inside the caliper by the pistons (only the chamber 25 delimited by the piston 24 appears in FIG. 1) are connected by flexible lines 26 and 27 to a hydraulic brake pressure transmitter such as a single or double brake master cylinder 28 (see Figure 2).

 During braking, under the action of the hydraulic pressure prevailing in the chamber 25, the piston 24 pushes a first friction lining 29 of fibrous material based on carbon fibers in contact with the face 30 of the disc 18 which slides by its grooves 19 on the grooves 17 of the ring 16 to come to bear on a second friction lining 31 bearing in a housing 32 on the left face (according to FIG. 1) of the brake caliper 20.

The brake disc 18 is thus clamped between the two friction linings 29 and 31 by the hydraulic pressure acting on the piston 24 to which the reaction force is opposed to the application of the friction linings 29 or 31 on the tracks of friction 30 and 30a d disc 18 and the reaction force of the part 33 connecting the two faces of the caliper.

 In Figure 2, there is shown in a fragmentary manner the brake caliper 20 for brake disc brake 18 of fibrous material of Figure 1. This caliper 20 includes the first brake cylinder 21 connected by line 26 to a first master cylinder 28a of the double master cylinder, as well as the brake cylinder 22 of smaller diameter than the cylinder 21 and which is connected by line 27 to a second master cylinder 28b of the double master cylinder 28. The pushers 34 and 35 of the master cylinders 28a and 28b are actuated in parallel by a balance 36 mechanically connected to a single brake pedal 37. In accordance with an embodiment of the invention, a "predominant" spring 38 (normally prestressed) is interposed around the pusher 34 between the balance 36 and a support flange 39 of the double master cylinder 28.

 The output of the first master cylinder 28a is connected to the supply line 26 for the brake cylinder 21 by means of a release valve or member 40 comprising an intake seat 41 which opens onto an intake chamber 42 permanently connected to an outlet pipe 43 to the pipe 26. A discharge chamber 44 is normally closed by a valve 45 pushed back into the closed position by a spring 46. The valve 45 is connected to the core 47 of an electro -magnet 48 electrically connected to an electronic control and command unit 49 to constitute a switching member.

The housing 49 which includes an electronic circuit for excitation of the electromagnet 48 is electrically connected to a temperature detector 50 which is normally repelled by a spring (not shown) in contact with the friction track of the disc 18, immediately downstream of the brake cylinder 21, in the preferential direction of rotation of the disc 18
(that of forward gear for a motorcycle or other mono-oriented vehicle). It will be noted that the brake cylinder 22 of smaller section is placed upstream of the brake cylinder 21 of large section, in the preferential direction of rotation represented by arrows. The boot 49 has a correction or sensitivity button 51 allowing the motorcycle driver to vary the temperature threshold which triggers the electrical or electronic threshold detector (not shown) mounted inside the housing 49 and triggers the excitation of the electromagnet 48 and , consequently, the opening of the valve 45 connecting the inlet chamber 42 to the discharge chamber 44 connected, for its part, to the discharge 52 (here constituted by the hydraulic fluid reservoir of the master cylinder 28).

 A fluid switching valve 53 makes it possible to interrupt the circuit of the loosening member 40 operating in an all or nothing mode and, by opening an annex circuit switching valve 54, to use a pressure divider 55 operating according to a mode proportional to two reais. The divider 55 is connected by a supply line 56 to the outlet of the master cylinder 28a which can advantageously be replaced (for industrial and railway vehicles, for example), by a compressed air pressure reducer.

 Line 56 is connected by an internal pipe to an inlet chamber 57 closed by a valve 58 bearing on an annular seat to isolate an outlet chamber 59 connected, via tap 54, to line 26. Inside of the pressure divider 55, a hollow tubular feed pusher 60 carrying a seat at its open end situated opposite the valve 58, is connected to two elastic membranes or actuating pistons 61 and 62, The piston 61 of small diameter delimits a control chamber 63 permanently connected to the outlet of the master cylinder or regulator 28a, while the intermediate chamber 64 located between the two membranes 61 and 62 is connected, on the one hand inside the tubular pusher 60 and, on the other hand, to the inlet chamber 42 of the release valve 40 and to the outlet pipe 43.

 The operation of the braking system described in Figures 1 and 2 will now be explained. When the driver of the motorcycle brakes at reduced speed, for example in the rain, the brake cylinders 21 and 22 are simultaneously supplied with brake pressure, the brake pressure of cylinder 21 of larger diameter being lower than that of cylinder 22 , of a substantially constant value due to the presence of the predominant spring 38. The coefficient of carbon-carbon friction is low, in particular in the rain, but the large section of the brake cylinder 21 re-establishes a correct braking torque.

 If the motorcycle driver brakes vigorously at high speed, the fuel valve; ic 53 being open while the valve 54 is closed to operate in an all or nothing mode, the brake cylinders 22 and 21 are supplied simultaneously with high braking pressures but initially only exert a moderate braking torque because the coefficient of friction remains low, of the order of 0.1. The slightly lower braking pressure (due to the predominantly spring 38) of the cylinder 21 however gives rise to a higher heating of the brake disc 18 at this cylinder 21 than at the level of cylinder 22 because the disc is preheated by the brake cylinder 22 placed upstream. The temperature sensor 50 thus senses outside the brake caliper 20 a temperature Tc substantially equal to the instantaneous temperature in contact between the friction lining applied by the cylinder 22 and the friction track of the brake disc 18. The adjustment button 51 of the electronic unit 49 has, for example, adjusted the direction threshold, bility Ts at 4000C at the sensor 50 while the transition temperature of the local friction torque used between the friction lining applied by the brake cylinder 22 and the disc 18 is, for example, T1 = 4450C, the temperature at the sensor 50 being in dynamics substantially equal to the temperature of the disc than 18 in front of the brake cylinder 22.

 When the braking is prolonged, the sensor 50 registers a temperature Tc greater than 4000C, the exceeding of the temperature threshold in the electronic unit 49 triggers the excitation of the solenoid of the electromagnet 48 constituting, with the electronic shoemaker 49, an electrical switching member and the switching of the valve 45 which closes the intake seat 41 and which, by detaching from the seat of the discharge chamber 44, connects the latter to the hydraulic fluid reservoir 52 constituting the discharge. pressure of the large-diameter brake cylinder 21 therefore disappears rapidly some tens of milliseconds after the temperature threshold at the sensor 50 is exceeded but, during this time, the heating of the friction contact continues and the latter exceeds the transition temperature T1 of 4450C, which leads to a coefficient of friction between the friction lining of cylinder 21 and the friction track which reaches values as high as 0.5. This substitution thus maintains the normal friction torque desired by the driver of the vehicle. When the surface of the disc cools, the sensor 50 again crosses, downwards, the temperature Ts of 400 "C and the electromagnet 48 is de-energized, which restores the brake pressure circuit shown in Figure 2 and allows the driver to have significant braking torque at the start of braking. When using marten cylinders 28a, 28b with manual control, the the driver is informed of the resumption of braking by the brake cylinder 21 because he perceives an additional sudden travel to the brake pedal 37 to refuel the cylinder 21.

 When the braking circuit is set to the pressure divider mode by closing the switching valve 53 and opening the valve 54, the development of the braking pressures is slightly different. At the start of cold braking, the braking pressure (which is for example pneumatic and can be transformed into hydraulic pressure by a pressure converter to actuate hydraulic brake calipers) is admitted simultaneously to the control chamber of 63 and to the intermediate chamber 64. The pressure of the intermediate chamber 64 pushes the tubular plunger 60 downwards and opens the valve 58 to supply, via the open valve 54, the brake cylinder 21 with the pressure delivered to the master cylinder or regulator 28a, if necessary via a pneumatic hydraulic pressure converter.

 As soon as the temperature at the sensor 50 exceeds the sensitivity threshold Ts fixed at 400 C in the example proposed, the tri-magnet 48 is de-energized and in fact connects the intermediate chamber 64 to the exhaust or to the discharge. The piston 61 of small diameter of the divider 55 then functions as a control piston balanced by the piston 62 of large diameter which functions as a reaction piston. The pressure prevailing in the outlet chamber 59 is then divided relative to the pressure emitted to the master cylinder 28a substantially according to the ratio of the active sections of the pistons 61 and 62. This solution makes it possible to use only one brake cylinder and however to cause a significant reduction in the effort of applying the friction linings to the friction tracks, this effort remaining proportional to the effort of actuation or control of the brakes by a vehicle driver.

 Various variants of the braking system according to the invention are possible. The master cylinders or pressure regulators 28a and 28b may each be capable of supplying the two brake cylinders 21 and 22, for example using a switching valve 65 or be replaced by a single master cylinder or regulator supplying the two brake cylinders 21 and 22. The master cylinders or regulators (including hydraulic pressure regulators) 28a, 28b, can be connected to the brake cylinders 21 and 22 by means of anti-clutch valves or anti-lock 66 with electronic control (not shown), these valves anyway releasing the brakes in the event that, the temperature sensor 50 or the electronic unit 49 no longer functioning, full pressure is applied to the cylinder 22 at beyond the transition temperature T1 at the friction contact. It is also possible to provide more than two brake cylinders and reverse the position of the cylinders 21 and 22 relative to the preferential direction of rotation of the disc 18 in order to achieve particular thermal effects on the brake disc 18. The sensor 50 can be integrated into the friction lining to better capture the maximum friction temperature.

 Of course, the present invention is not limited to the embodiments described and shown, but it is capable of numerous variants accessible to those skilled in the art without departing from the spirit of the invention.

Claims (8)

 1.- Braking system for a vehicle using at least one brake disc or equivalent of which at least the friction track is made of a material such as carbon fibers, having a coefficient of friction which increases rapidly when the temperature at the friction contact exceeds a predetermined threshold value (Ts), this device comprising at least two separate brake application members, but actuated simultaneously by the driver of the vehicle, characterized in that it further comprises a detector (50) of the temperature of the friction track in said clamping members (21, 22) or immediately downstream of them and in that said detector is coupled, via a temperature threshold detector (49) , to a release member (40, 55) able to release at least partially and significantly one (21) of the two brake clamping members, called the first clamping member, when the track temperature friction detected by the threshold detector (49) is close to, but less than, said threshold temperature (Ts) and has triggered, via the threshold detector, a switching member (48).  2. Braking system according to claim 1, characterized in that the release member (40) is a distributor of the brake fluid for applying the brakes of said first clamping member (21), comprising an inlet and two outlets: one towards said first clamping member (21) and the other towards the discharge (52), an electromagnetically controlled distributor member such as a valve (45) being able to connect said first clamping member (21) either to a brake pressure transmitter (28 'actuated by the driver of the vehicle, that is, when the switching member (48) is triggered to activate said electromagnetic control, to discharge with closure of the input.  3.- braking system according to claim 1, characterized in that the release member (55) is a divider of the braking pressure electrically controlled by the switching member (48), the second braking member ( 22) being, where appropriate, deleted.  4.- braking system according to any one of claims 1 to 3, characterized in that, when the brake clamping members are actuated by a fluid pressure1 the first clamping member (21) has an efficiency proportional to that of the other brake clamping member (22), called the second clamping member, but larger than that of this second clamping member, using any suitable means such as: larger brake cylinder section, pressure of higher braking, friction lining with higher coefficient of friction.  5. Braking system according to any one of claims 1 to 4, characterized in that the switching member (48, 49) is adjustable by the driver of the vehicle to allow him to vary (button 51) the threshold temperature and / or the trigger threshold of the cornsr.utation organ (48, 49).  6. Braking system according to any one of claims 1 to 5, characterized in that the actuating member (34, 36) of the control (28a) of the first braking member (21) cooperates with at least a predominantly spring (38) capable of reducing the braking pressure of the first braking member (21) relative to that of the second braking member (22) by a substantially constant value.  7. Braking system according to any one of claims 1 to 6, characterized in that the detector (50) of the temperature of the friction track is repelled by an elastic member in rubbing contact with the friction track, immediately downstream of the first braking member (21) which is itself placed downstream of the second braking member (22) relative to the preferential direction of rotation of the brake disc (18).  8.- braking system according to any one of claims 1 to 7, characterized in that it comprises a switching valve (65) capable of connecting the brake pressure fluid circuit of the second braking member (22) either only to the second braking member, or simultaneously on the one hand to the second braking member (22) and on the other hand to the first braking member (21), via the release member (40, 55).